Permanent magnet probe flowmeter

ABSTRACT

A probe-type flowmeter for measuring the flow of conducting fluids, in particular liquid sodium, is described. The probe includes a permanent magnet for developing a magnetic flux and a pair of conductors coupled to a metering device for measuring the e.m.f. developed in the conducting fluid. The magnitude of the e.m.f. is a function of the fluid velocity.

- United States Patent [1 1 Wood et al. 1 June 5, 1973 54 PERMANENTMAGNET PROBE 3,487,826 1/1970 Barefoot ..73/194 EM ux 3,516,399 6/1970Barefoot ..I28/2.05 F FLOWMETER 1,249,530 12/1917 Smith et aL.....73/194 EM UK [75] Inventors: Myrick R. Wood, Richland; Bernard2,149,847 3/1939 KoIin ..73/l94 EM H. Duane, Pasco; Delbert L. Lessor,Richkmd a of wash FOREIGN PATENTS OR APPLICATIONS 73 Assigneez TheUnited States of America as 1,248,606 3/1971 U.S.S.R. ..73/194 EMrepresented by the United States Atomic Energy Commission, PrimaryExammerChar1es A. Ruehl Washington, DC Attorney-ROIand A. Anderson [22]Filed: June 24, 1971 57] ABSTRACT 21 App No.: 74,384 1 A probe-typeflowmeter for measuring the flow of conducting fluids, in particuiarliquid sodium, is [52] US. Cl. ..73/194 EM described. The probe includesa permanent magnet [51] Int. Cl ..G0lf 1/00, GOIp 5/08 for developing amagnetic flux and a pair of conduc [58] Field of Search... ..73/194 EM;tors coupled to a metering device for measuring the 128/205 F e.m.f.developed in the conducting fluid. The magnitude of the e.m.f. is afunction of the fluid velocity. 56] References Cited UNITED STATESPATENTS 8 Claims, 7 Drawing Figures 3,114,260 12/1963 SoIler et al..73/I94 EM X PERMANENT MAGNET PROBE FLOWMETER CONTRACTUAL ORIGIN OF THEINVENTION BACKGROUND OF THE INVENTION In order to properly operate manyheat-generating devices, it is necessary that the flow of various fluidsthrough the apparatus be measured. This is particularly true in reactorsusing liquid sodium as the coolant, where the loss of coolant flow canlead to dangerous reactor conditions. In a reactor it is often desirableto use a probe type of flowmeter in measuring the flow of sodiumcoolant, as the outside of the coolant pipes is not always accessible toexterior-type flowmeters. The probe-type flowmeter is inserted directlyinto the pipe through which the fluid flows to measure the fluid flowvelocity inside the pipe. This type of flowmeter must therefore becapable of withstanding the liquid sodium environment, that is, a verycorrosive and very hot environment.

In addition, in order to operate reactors using liquid sodium as acoolant safely, it is necessary that large numbers of flowmeters be usedso that any flow failure can be measured quickly and corrective actiontaken. It is therefore desirable that any flowmeter used be of simpleand rugged construction so that large numbers of flowmeters will not betoo expensive.

It is therefore an object of this invention to provide an improved typeof flowmeter which can be inserted as a probe in a coolant pipe.

Another object of this invention is to provide a flowmeter which issimple and rugged in construction and inexpensive.

Another object of this invention is to provide a flowmeter which canwithstand high temperatures and a corrosive environment.

SUMMARY OF THE INVENTION In practicing this invention, a permanentmagnet is enclosed in a tube resistant to the corrosive environment ofliquid sodium. The permanent magnet is magnetized so that the lines offlux therefrom are perpendicular to the flow direction of the fluid. Apair of leads are electrically connected to the sodium fluid to measurethe voltage developed in the sodium fluid as it flows through the linesof magnetic flux. Metering devices are attached to the pair of leads inorder to measure this voltage which is a function of the flow velocityof the conducting fluid. No apparatus is required outside of the tube atthe point where the measurement is to be made and the probe does nothave to make contact with the tube walls. Thus the flowmeter probe canbe inserted and removed from the tube easily.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is illustrated in thedrawings, of which:

FIG. 1 is a cross-sectional view of the flowmeter of this inventionshown in position in a pipe;

FIG. 2 is a cross-sectional view of the pipe and flowmeter of FIG. 1;

FIG. 3 is a view of the permanent magnet structure of the flowmeter ofFIGS. 1 and 2;

FIG. 4 shows an alternate construction for the electrodes of FIGS. 1 and2;

FIG. 5 shows an alternate construction of the flowmeter in which theelectrodes are mounted outside of the flowmeter body;

FIG. 6 is a cross-sectional view of the electrodes of FIG. 5 showing theelectrode construction; and

FIG. 7 is an alternate form of the flowmeter of FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIGS. 1 to 3, thereis shown the permanent magnet flowmeter of this invention. A permanentmagnet probe flowmeter allows flow velocity measurement of conductingliquids in tubes and uses no apparatus outside the tube near thelocation of the probe. The flowmeter can be inserted into the tube andremoved as desired. The flowmeter has a positioning projection 12 whichis inserted in a holder 15 placed in tube 10. The fluid in tube 10 flowsin the direction indicated by the flow arrows 11 and is a conductingfluid such as liquid sodium.

The probe housing 13 is made of a nonferromagnetic material such as astainless steel and encloses the magnet and electrodes of the probe. Theprobe housing material is of a type which will withstand the temperatureand corrosive properties of the fluid in the pipe 10.

A permanent magnet 14 is contained within the probe housing 13 and ismagnetized to develop a flux in the tube 10 perpendicular to thedirection of flow velocity of the fluid in tube 10, as shown by themagnetic field lines 27 and 28. Permanent magnet 14 contains two holes16 and 17 which permit the wires connected to the electrodes required tomeasure the e.m.f. gener' ated in the fluid to be placed in the properposition in the probe 13. Wires 19 and 20 pass through hole 16 and aresplit with one being electrically connected to the inside of probe 13 atpoint 24 and the other wire being electrically connected to the insideof probe 13 at point 25 to form the electrodes. The electric potentialbetween points 24 and 25 is measured by voltmeter 22 which is connectedto wires 19 and 20. If the permanent magnet is housed within aconducting material such as stainless steel, the electrodes 24, 25 canbe connected to the inner surface of the probe. If the probe material isnonconductive, the contacts can protrude through sealed holes or can bepositioned outside, as will be described in a subsequent portion of thespecification.

The magentic field, as shown by the flux lines 27 and 28 of FIG. 2, issubstantially perpendicular to the flow direction of the fluid in pipe10 and has an axis of symmetry 29. The magnetic fields on opposite sidesof the axis of symmetry outside of the permanent magnet are different.In the example of the magnetic field shown in FIG. 2, the field isclockwise on the right side and counterclockwise on the left side of theaxis of symmetry. These field directions could be reversed if desired.The electrodes 24 and 25 are positioned on opposite sides of the axis ofsymmetry 29.

The permanent magnet flowmeter measures the velocity of a fluid bymeasuring the electrical potential difference developed between twopoints in a conductive fluid moving in a magnetic field. Thus thepotentials outside of the probe 13 at points 24 and 25 are different andthe potential difference is measured by voltmeter 22. The magnitude ofthis potential difference is a function of the flow velocity of thefluid in pipe 10. The maximum sensitivity of the flowmeter is achievedwhen a line joining the points of contact 24 and 25 is substantiallyperpendicular to the axis of symmetry 29 and the flow direction;however, the contacts can be located at other positions on oppositesides of the axis of symmetry.

The ends of the permanent magnet 14 produce flux lines which are notperpendicular to the flow direction and thus contribute noise to thesignal being measured. It has been found that this noise can beminimized to a point where it is not an important factor if the length lof the permanent magnet is at least four times the diameter d of thepermanent magnet. The electrodes 24 and 25 are then positioned midway ofthe length l of the permanent magnet 14.

Referring to FIG. 4, there is shown a form of the flowmeter probe inwhich the walls of the housing 31 are formed of a material which is notconductive. In this case, the electrodes 34 and 35 penetrate the housing31 through sealed holes and make direct contact with the fluid outsideof the probe housing. The probe material need only be nonferromagneticso that the magnetic field penetrates into the fluid.

Referring to FIG. 5, there is shown a view of a probe 32 similar inconstruction to the probe of FIGS. 1 to 3. However, in probe 32 theelectrodes 37 and 38 are positioned outside of probe 32 in directcontact with the fluid. With this form of construction the material fromwhich the probe 32 is manufactured need not be conductive but only needbe nonferromagnetic so that the flux lines of the permanent magnetcontained therein will penetrate into the fluid.

Referring to FIG. 6, there is shown an enlarged view of one of theelectrodes 37 and 38 of FIG. 5. The interior wire 41 of the electrode iselectrically connected to the conductive sheath 40 at point 42 only. Thewire 41 is insulated from all other points of the sheath 40 byinsulation 43. The voltage on wire 41 is the potential in the fluid atpoint 44 on the sheath. The end 44 of sheath is placed at a desiredposition in the fluid to measure the fluid velocity at this point.

Referring to FIG. 7, there is shown an alternate form of the probesimilar to that of FIG. 5. In FIG. 7, electrodes 47 and 48 of probe 49are bent outward away from the body of the probe. The ends of electrodes47 and 48 are the same as shown in detail in FIG. 6. By placing the endsof the electrodes out away from the probe body, the probe measures thevelocity of the fluid through the pipe unaffected by any stagnantboundary layer which may be next to the probe body The embodiments ofthe invention in which an exclusive property or privilege is claimed aredefined as follows:

)1. A permanent magnet flowmeter for measuring the 4 velocity of aconducting fluid, comprising, a probe positioned entirely within thefluid, said probe including a permanent magnet for developing a magneticfield Within the fluid with the direction of said magnetic field in saidmagnet and in said fluid being substantially perpendicular to the flowdirection of the fluid, said magnetic field having an axis of symmetryperpendicular to said flow direction with said magnetic field outside.of said permanent magnet having a clockwise direction on one side ofsaid axis of symmetry and a counterclockwise direction on the other sideof said axis of symmetry, said probe further including a pair ofelectrodes positioned on opposite sides of said axis of symmetry and inelectrical contact with the fluid, and means connected to said pair ofelectrodes for measuring the potential therebetween.

2. The flowmeter of claim I wherein, a line joining said pair ofelectrodes is substantially perpendicular to said axis of symmetry andsaid flow direction.

3. The flowmeter of claim 2 wherein, said probe includes a housing of anonferromagnetic material and having a circular cross sectionperpendicular to said flow direction, said permanent magnet beingpositioned within said housing and having a cylindrical shape with thecylinder axis substantially parallel to said flow direction, saidpermanent magnet being magnetized so that said axis of symmetry isperpendicular to said cylinder axis.

4. The flowmeter of claim 3 wherein, the length of said cylindricalpermanent magnet is at least four times the diameter thereof.

5. The flowmeter of claim 4 wherein, said housing is electricallyconductive, said electrodes being in contact with the inside of saidhousing and positioned at substantially the midpoint of the length ofsaid permanent magnet.

6. The flowmeter of claim 3 wherein, said electrodes extend through saidhousing and are in direct electrical contact with said fluid. I

7. The flowmeter of claim 3 wherein, said electrodes are positioned onthe outside of said housing, each of said electrodes being enclosed in aprotective electrically conductive sheath and being electricallyinsulated therefrom, each of said electrodes further being electricallyconnected to said enclosing protective sheath at one point with a linejoining the points at which said electrodes are connected to said sheathbeing substantially perpendicular to said axis of symmetry.

The flowmeter of claim 7 wherein, said points of said sheaths at whichsaid electrodes are electrically connected to said sheaths are spacedaway from said housing a predetermined amount.

'3 k 3' t! t

1. A permanent magnet flowmeter for measuring the velocity of aconducting fluid, comprising, a probe positioned entirely within thefluid, said probe including a permanent magnet for developing a magneticfield within the fluid with the direction of said magnetic field in saidmagnet and in said fluid being substantially perpendicular to the flowdirection of the fluid, said magnetic field having an axis of symmetryperpendicular to said flow direction with said magnetic field outside ofsaid permanent magnet having a clockwise direction on one side of saidaxis of symmetry and a counterclockwise direction on the other side ofsaid axis of symmetry, said probe further including a pair of electrodespositioned on opposite sides of said axis of symmetry and in electricalcontact with the fluid, and means connected to said pair of electrodesfor measuring the potential therebetween.
 2. The flowmeter of claim 1wherein, a line joining said pair of electrodes is substantiallyperpendicular to said axis of symmetry and said flow direction.
 3. Theflowmeter of claim 2 wherein, said probe includes a housing of anonferromagnetic material and having a circular cross sectionperpendicular to said flow direction, said permanent magnet beingpositioned within said housing and having a cylindrical shape with thecylinder axis substantially parallel to said flow direction, saidpermanent magnet being magnetized so that said axis of symmetry isperpendicular to said cylinder axis.
 4. The flowmeter of claim 3wherein, the length of said cylindrical permanent magnet is at leastfour times the diameter thereof.
 5. The flowmeter of claim 4 wherein,said housing is electrically conductive, said electrodes being incontact with thE inside of said housing and positioned at substantiallythe midpoint of the length of said permanent magnet.
 6. The flowmeter ofclaim 3 wherein, said electrodes extend through said housing and are indirect electrical contact with said fluid.
 7. The flowmeter of claim 3wherein, said electrodes are positioned on the outside of said housing,each of said electrodes being enclosed in a protective electricallyconductive sheath and being electrically insulated therefrom, each ofsaid electrodes further being electrically connected to said enclosingprotective sheath at one point with a line joining the points at whichsaid electrodes are connected to said sheath being substantiallyperpendicular to said axis of symmetry.
 8. The flowmeter of claim 7wherein, said points of said sheaths at which said electrodes areelectrically connected to said sheaths are spaced away from said housinga predetermined amount.